It is well known to transport wind turbine blades one by one on trucks and by ship. It has also been common to transport more than one wind turbine blade on e.g. the same truck. But as the wind turbines grow larger and larger also the wind turbine blades have become wider and longer, and in 1997 wind turbine blades having the tip end pointed forward and into the wind was invented. Wind turbine blades with this feature are commonly known as pre-bend wind turbine blades, as the unloaded blade is curved.
When a pre-bend blade during use is loaded, it will be straightened, instead of swept back, and this will allow the rotor to be arranged closer to the tower and still maintain a reasonably tip to tower distance. The tip to tower distance is actually the main advantage of the pre-bend blades, and over time this has more or less become the standard for modern and large wind turbine blades. Especially when talking about wind turbine blades having a length of more than 35, 40, 45 or even more than 50 meters.
One disadvantage using pre-bend blades is however very clear when it comes to transportation, especially by road. As the blades no longer are as straight as they used to be, they take up considerably more space in both the width direction and in the height direction. This has been handled in various manners, but one very used method has been to transport such pre-bend wind turbine blades one by one using a truck with a flatbed trailer and a following safety car.
The term flatbed trailer is to be understood as a general term comprising the various types of trailers having a more or less flat carrier surface including Drop Deck, Double Drop Deck, Step Deck and other types of trailers.
The blades are transported one by one by a truck on a flatbed trailer, and if the blades have to be shipped, they will be transported to the harbour using trucks as described, and the blades will be hoisted onto the ship and secured to the deck one by one. The wind turbine blades will typically be fitted with a frame or a foot at the root end and further there will typically be some kind of support structure at the outermost portion of the blade e.g. at ⅔ of the blade length when measured from the root end.
As the wind turbine blades often have to be transported quite some distance, and as such transports only carry one wind turbine blade per truck followed by a safety car, there will typically be a need for three independent trucks and safety cars per wind turbine. This will of course induce considerable costs.
It is thus interesting to optimise such transports in general with regard to the costs but also with regard to efficiency, meaning the time spent per transported wind turbine blade. One further problem to be addressed is the place taken up by the wind turbine blades during transport by road but also by ship.